I don't wear any of the types of shorts depicted in your picture...and I don't ever wear flip flops - because they're gαy.
Bishop Williamson has an "opinion" on shorts...that's all it is man - an opinion.
Nor do we have any context around this reported opinion. Are there exceptions, conditions, distinctions? Would he even consider pants that just extended to below the knees to be "shorts"?
I'm just looking for a rational argument.
So far we have:
1) Bishops Williamson said boys should not wear them (no context around what he said and it's his opinion for reasons unknown to us).
2) They're effeminate either because of the style or because they turn boys into sissies. [I don't buy this.]
3) "Shorts" = "bad" (just like with Trump: Orange Man is bad.) just a triggered reaction without any rationale behind this, with shorts being associated in people's minds with being shorter than those depicted and therefore immodest.
I'm unconvinced.
That flip-flops and certain types of shorts look gαy. I grant that. But the shorts worn by the boys in the OP's picture do not fall into that category ... IMO.
Whether something is effeminate or not can be argued, and it's partly a subjective thing. Some of that is culturally-relative. I personally find kilts to look effeminate, but that's due to my cultural perception that that style of dress is proper to women. I find some of the extremely flowery uniforms of Eastern European men to be somewhat effeminate. Some cultures considered being clean-shaven to be inherently effeminate. That's why missionary priests invariably grow beards, because they tend to be perceived as effeminate girly-men by the natives and would never be taken seriously or respected. I honestly had a difficult time with the cassock because in the U.S. the perception is that you're wearing a dress, and with all the ɧoɱosɛҳųαƖ Novus Ordo presbyters out there, this was rather uncomfortable for me. I wore pants underneath and had a cassock just short enough that you could see the bottom of the pant legs. Now, if you were in Europe, everybody recognizes what you're wearing. But in the U.S. the perception is one of effeminacy. I know that the Nine (and their descendants) don't wear cassocks in public, saying that it was the custom in the U.S. for priests and clerics to wear pants. But the SSPX imported European customs into the U.S.